Muscles involving respiration


The muscles which are entangled with the process of respiration, for the most part, experience involuntary automatic rhythmic contractions in tune with the natural course of breathing. Pulmonary ventilation, which is the technical term given to the process of breathing, is segregated into two categories based on whether the body is inhaling or exhaling.

During a period of relaxed and average respiration, the muscles associated with inspiration, or the process of inhaling, include the muscles of the diaphragm, the external intercostal muscles, and the interchondral region of the internal intercostal muscles.


The diaphragm, which is in the basic shape of a dome or semicircle, is known to contract downward, causing the necessary vertical increase in the thoracic dimensions. The muscles of the external intercostal muscles and the appropriate muscles of the internal intercostal muscles contract as well, in timed rhythm to the contraction of the diaphragm.

This creates a simultaneous increase in the lateral thoracic dimensions. When necessary, the scalene muscles and the sternocleidomastoidal muscles join in, contracting when the first and second ribs need to be elevated in order to permit the natural process of inhalation.


Muscles of Respiration
Image: Muscles Of Respiration

Intercostal nerves take care of the required innervating of the intercostal muscles while the phrenic nerves innervate the diaphragm.


The process of expiration is a natural reflex associated with respiration, and often requires no assistance from the muscles beyond the natural relaxation of the involved muscles, which enhances expiration. The muscles simply relax their contraction and the air is eased from the lungs.

In the event of forced expiration there is an additional muscle contraction of the interosseous section of the internal intercostal muscles which results in the depression of the rib cage. This of course assists in the forced expulsion of air. These muscles are located under the external intercostal muscles. The fibers of these muscles are intentionally laid in a down and backward layering. In large scale forced expiration, the abdominal muscle join in the efforts, contracting enough to increase abdominal cavity pressure and direct the diaphragm toward the superior quadrant in order to help the lungs rid themselves of air quickly.
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